Any existing electronic component is characterized by an electrical power absorption—in general, proportional to the product of a current crossing it and a voltage that develops between its terminals—during the operation of the same. A portion of the absorbed power is lost as heat according to the principles of thermodynamics. In particular, heat is generated in the “active” regions of the electronic component, i.e. where the flow of electric current occurs (for example, considering a MOS, IGBT or BJT transistor, in a region below a controlling terminal and in the regions constituting conduction terminals of the same). The generation of heat concentrated in active regions causes a temperature rise of the electronic component. The temperature of the active regions of the electronic component, better known as the junction temperature, is a parameter that strongly affects the operation of the electronic component.
For example, the threshold voltage of a MOS transistor (whose value determines the amount of current flowing in the transistor with the same control voltage applied) is inversely proportional to the junction temperature. Consequently, with the same control voltage applied, the MOS transistor draws an ever-increasing electric current flow as the temperature rises. It is also known that, with increasing junction temperature, the electrical resistance of the MOS transistor increases. Consequently, the MOS transistor dissipates between its terminals, due to the Joule effect, an ever-increasing electric power. Because of this, the junction temperature rises even more. In other words, there is established a positive feedback (better known as thermal runaway) that can cause damage or even the destruction of the MOS transistor. In addition, with the rise of the junction temperature of the MOS transistor there is a reduction of the reliability of the same (i.e., the probability of occurrence of a structural damage during the operation increases) and in general of its working life (i.e., the time for which the electronic component works properly).
The ongoing miniaturization process of the electronic components (basically a reduction in the size of the electronic component, in particular of the active regions), makes it very important to contain the rise in junction temperature within acceptable values. In fact, with the same absorbed electric power, the smaller the size of the active region of the electronic component, the higher and faster the rise in junction temperature in the same (since the dissipation of electrical power is concentrated in a smaller volume). This is particularly important for electronic components belonging to the field of the “power electronics”, i.e. electronic components designed to operate at higher voltages and currents than standard electronic components (for example, with operating voltages of the order of hundreds of Volts and/or with operating current in the tens of Amperes), which are used in circuits of apparatuses belonging to various fields of application, for example, from personal computers to electro-mechanical equipment (power supply circuits of computers, electric motors actuators, inverters for photovoltaic panels, etc.).
In order to contain the rise in junction temperature in electronic components, heatsinks are known and widely used. A heatsink is an element consisting of one or more elements in thermally conductive material (e.g., aluminum), which is attached (typically by gluing) to a package of the electronic component. The package substantially comprises an insulating body (usually in plastic or ceramic) and contact pins (to connect the electronic component to tracks of an external circuit), and is intended to incorporate and protect a chip of semiconductor material wherein the electronic component is integrated.
Alternatively, the insulating body of the package may also comprise an opening—typically formed in an upper free surface of the insulating body opposite to a mounting surface towards which the pins are oriented—for exposing a dissipation plate (also made of thermally conductive material). The dissipation plate is connected to the chip of semiconductor material for improving the heat exchange with the external environment. The heatsink may be attached directly to the dissipation plate, thus facilitating a conductive heat exchange between the chip and the heatsink (thanks to the greater thermal conductivity of the materials constituting the dissipation plate and the heatsink in contact with each other with respect to the plastic ones forming the insulating body).
In more detail, the heatsinks facilitate a heat transfer by conduction (thanks to its good thermal conductivity) from the chip to itself. Furthermore, heatsinks are typically formed with a structure designed to facilitate a heat transfer by convection (for example, with a plurality of fins extending from a base through which the heatsink is attached to the insulating body or to the dissipation plate) to the environment external to the package (i.e., transferring heat to the medium that surrounds the package, for example, air). In this way, suitably sized heatsinks allow for maintaining the junction temperature below a safe temperature.
However, the heatsinks suffer from a major disadvantage, particularly when applied to small packages (for example, for incorporating miniature electronic components). In fact, the heatsinks tend to be mechanically unstable, once fixed to the package. This is due to the fact that, by reducing the package size, the available mounting surface is proportionally reduced. This reduced mounting surface may be insufficient to ensure a good mechanical stability of the heatsink on the package; consequently, the heatsink might separate from the package as a result of mechanical stresses to which it may be subjected. In addition, the weight of the heatsink and the mechanical stress may be likely to cause a deterioration, or even a breakage, of contacts formed between one or more pins of the package and the corresponding tracks to which they are attached, at most provoking their detachment and the failure of a circuit in which the electronic component is used.